Cathode ray tube



. P 5 E. R. WOUGHTER ETA]. 2,906,904

CATHODE RAY Filed April 17, 1956 INVENTORS Earl R. Woughter 8: William J. Knochel BY WITNESSES I g ATTORNEY United States Patent CATHODE RAY TUBE Earl R. Woughter, Elmira Heights, and William J.

Knochel, Elmira, N.Y., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application April 17, 1956, Serial No. 578,624

2 Claims. (Cl. 313-85) This invention relates to cathode ray tubes and, more particularly, to electron beam shields for use in cathode ray tubes.

In cathode ray tubes, such as those used in television receivers, electrons emitted by electron beam generating means impinge upon a luminescent screen in such a manner as to excite the luminescent screen which emits light. More particularly, in a shadow mask color television tube as described in a copending application entitled Color Television Tube by William J. Knochel, Serial No. 564,- 720, filed February 10, 1956, now Patent 2,871,087 and assigned to the same assignee as the subject application, the luminescent screen is comprised of a plurality of groups of phosphor dots which emit different colors, e.g., red, green, and blue when they are excited by the impinging electrons. The electrons are emitted by an electron beam generating means, such as an electron gun or plurality of electron guns and are deflected by suitable deflecting means, e.g. magnetic fields supplied by coils external to the tube, in order to scan a suitable pattern. After the electrons are deflected, they travel in straight lines through a relatively field free region, pass through apertures in a shadow mask electrode and finally strike a phosphor dot which will emit the desired color. The apertures of the shadow mask electrode are in registration with the corresponding phosphor dot groups. To obtain pure saturated colors it is essential that an electron beam intended to excite, for example, red phosphor dots hit only these dots and that no other electrons arise within the tube which can strike and excite unwanted colors. The alignment and registration of the electron beam source, which is considered to include the deflecting means, the shadow mask apertures and the phosphor dots is, therefore, very critical 'and must be accurately done.

We have found that stray electrons may be generated .within the cathode ray tube due to various causes. One cause of stray electrons is-scattering when the primary electron beam hits the side walls of the envelope of the cathode ray tube at the extremities ofthe scanning pattern. Unless these scattered electrons are prevented from doing so, they may pass between the edge of the shadow mask electrode and the envelope wall and possibly after further scattering, collisions with the mask and the envelope wall, may excite the several phosphor colors of the luminescent screen more or less equally. sults in an array of the generally whitish illumination which strongly desaturates colors and degrades contrast. This effect is especially objectionable in the rounded corners of the so-called rectangular cathode ray tube enevelope which is normally used in the television industry. The rectangular scanning pattern may cause many This re- 2,906,904 Patented Sept. 29, 1959 ice envelope wall itself since the lateral positioning of the shadow mask electrode must be established by the various glass and metal positioning and locating means described in the above-mentioned copending Knochel application, which lateral positioning is done independently of the location and shape of the shadow mask rim and cathode ray tube envolpe wall.

It is accordingly an object of this invention to provide an improved cathode ray tube which produces a picture with improved contrast.

It is another object to provide an improved color cathode ray tube which produces a picture with improved color resolution.

It is a further object to provide an electron beam shield for a cathode ray tube.

It is still another object to provide an embossed electron beam shield for a cathode ray tube.

It is a still further object to provide an improved electron beam shield for a cathode ray tube which beam shield is comprised of a metallic foil material.

These and other objects of our invention will be apparent from the following description taken in accordance with the accompanying drawing throughout which like characters indicate like parts, which drawing forms a part of this application, and, in which:

Figure 1 is a perspective view, partly in section, of a cathode ray tube embodying our invention;

Fig. 2 is a plan view of the inside of the faceplate portion;

Fig. 3 is a sectional view of a detail portion of one embodiment of our invention;

Fig. 4 is a perspective view of a detail portion of another embodiment of our invention;

Fig. 5 is a sectional view of a detail portion of Fig. 4 as seen from the rear;

Fig. 6 is a detail view of a portion of Fig. 5, and

Fig. 7 is a plan view (of a detail portion) of another embodiment of our invention.

Referring in detail to Fig. 1, there isshown a cathode ray tube embodying our invention including an envelope member 11 which includes a face panel portion 13 and a funnel portion 19. The face panel portion .13 includes a faceplate portion 15 and a skirt portion 17. The funnel portion 19 includes a flared portion 21 and a neck portion 23. A luminescent screen 25 has been deposited upon the faceplate portion 15. Electron beam generating means 27 have been positioned in the neck portion 23 and generate electron beams 29, which, after traveling through shadow mask electrode apertures 33 of a shodaw mask electrode 31, impinge on the luminescent screen 25 which is comprised of a number of phosphor dots 35. For simplicity, only one aperture 33 and a few dots 35 of the screen 25 are shown. A conductive coating 39 has been applied to'the interior of the envelope member 11 and the face panel portion 13 has been sealed to the funnel portion 19 at a seal portion 41. An electron beam shield member 37, which will be more fully described below,

has been inserted betweenthe shadow mask electrode 31 and the electron beam generating means 27. This electron beam shield member 37 intercepts undesirable scattered electrons which may arise, for example, when electron beam 29 strikes the envelope wall and which would create undesirable edge effects, and impurity of color if they were allowed to strikethe luminescent screen 25. This electron beam. shield 37 also eliminates the possibility of an are forming between the luminescent screen 25 and the seal portion 41 during the electric seal 3 process described in *the Knochel "application "entitled Color Television Tube referred to previously.

Fig. 2 shows a plan view of the inside of the face panel portion 13 with the shadow mask electrode 31 in position and showing the skirt portion 17. The electron beam shield member 37 is positioned on top of the shadow mask electrode.31'as will'be described below. Also shown are integral lockin projection members 13 which will b'e'more 'fully described below.

:In.Fig. 3 there is shownaside sectional view of a detail of a cathoderay tube showing-'how the electron beam shield member 37 may be positioned in one embodiment of our invention. The face panel portion 13 of the 'envelope 11 is shown including the skirt portion 17 and a part of the faceplate portion 15. The shadow mask electrode 31 rests upon a support land member 45. A fastening spring member 47 is inserted into a'notch '59 in a lock-in projection member 43. The fastening spring member 47 is also attached to a hold-down 'ring member 49 to which is iattached an electron beam shield positioning member 51 which holds the electron beam shield member 37 against the shadow mask electrode 31. A suitable material -for the fastening spring member 47 is spring temper metalsold underthe trademark Inconel. The electronbeam shield positioning member'Sl 'may'also be made of Inconel and maybe of either wire or flat stock. If desired, the hold-down'spring member 49 may be a wire to which an lnconel leaf spring electron beam shield positioning member 51 is welded.

The electron beam shield member may be made of aluminum having a thickness of .010 to .0015". This aluminum may be stamped from aluminum sheeting of desired thickness and after -proper cleaning it may be inserted into the cathode ray tube. An aluminum electron beam shield member 37 will allow direct contact with the glass envelope member 11 thereby giving complete electron beam shielding because the electrons are not'allowed to pass between the electron beam shield member 37 and the skirtportion of theenvelope member 11. 'Also aluminum will not damage the glass during the heating cycles in the manufacture ofcathoderay tubes, thus eliminating a source of possible breakage.

In Figs. 4, '5 and 6 thereare shown portions of the part of the face panel portion 13-including the skirt portion'17 and-thefaceplate portion 15. The shadow mask electrode :31 is positioned upon 'a support land member 45 and the electron beam shield member '61 is held by a one piece electron beam shield positioning member 53. As can 'beseen, a portion of this electron beam shield positioningmember '53 is inserted in the notch 59 of the lock-in projection member 43. Another portion of'the electron beam shield positioning member holds the elec 'tron'beam shield :member 61 in touching relationship to the shadow mask'electrode 31. 'We have found it desirableat'times to emboss'a'porti'on 55 of the electron beam shield member 61 where the electron beam shield positioning member 53holds the electronbeam shield member 61 against .the shadow mask 31. Therefore, it is seen that the electron beam shield member 61 touches the shadow mask 31 only at the embossed positions. This isadvantageous because if the electron beam shield member 61 and shadow mask electrode 31 were required to be in touching relationship for large portions of their area, a perfect match would be required in order to prevent distortion of the shadow mask and the resultant color impurity. With small portions of the two members touching each other atthe points where the shadow mask 31 rests on the support "lands 45 or other mask support means, any slight deviation on the construction of the electron beam shield member 61 will not distort the shadow mask '31. Theembossed portions 55 of the elec tron beam shi'eldmember 61 also providesan easy means of checking the seating of the electron beam shielding positioning member.

In Fig. 7 there is shown another embodiment of our invention'in*which"portions of electron'beam shield members 57 are used rather than the electron beam shield member 37 or 61 shown in previous figures. The skirt portion 17 of the face panel portion 13, the shadow mask electrode 31 and the electron beam shield positioning members 53 are also shown. The partial electron beam shield member 57 as shown in Fig. 7, has in some instances, proven to provide suflicient electron beam shielding when located in the corner portions of the shadow mask electrode 31. This is primarily because the standard rectangular scanning pattern causes extensive bombardmentof the tube walls at the rounded corners of the customary 'znominally rectangular glass .tube envelope. It has also 'been found that the shadow mask electrode 31 may be positioned more closely to the glass envelope 11 in the flatter portions of the peripheryof the shadow mask electrode 31 but it is difficult to make such a close fit in the corners of the shadow mask electrode 31.

We have also found that in some instances that it may be desirable to make the electron beam shield member 37 of thinaluminumfoil such :as that knownas Reynolds Wrap. We have found that if this .thin aluminum foil is cut in strips having a width of approximately 6 inches and is folded'twicelleaving a strip 1 /2 inches wide with the thickness 4 times the original foil, this latter strip maythen be formedaround a die to the desirable shape. After the'shadow'mask.electrode31 has been permanently inserted in the cathode .ray tube the electron beam shield member.37 is then positionednext to the mask electrode 31Iand is held by positioning means as described above or by-anyother means. vAfter the electron beam shield member 37 is fastened in position, .it may be placed againstthe glass envelope 11 thus filling thegap between theshadow mask electrode 31 and theskirt portion 17 of the face panel portion 13. Thus, this foil electron beam shield member .37 provides the necessary electron beam shielding as wellas the arc protection of the luminescent screen '25. Also, the aluminum foil electron beam shield member 37 does not distort the shadow mask electrode 31 during heating cycles and 'does not scratch theglass panel. We have found that an electron beam shield member 37 made of aluminum foil holds its shape during the steps of preheating, electric sealing, annealing, exhaust and bake-out and while operating as a cathode ray tube. As can also be seen, it can be produced easily and cheaply.

Another advantage of using the fastening means described above is that the mask is allowed to breathe during the sealing and annealing cycles, therefore following more closely th'edirect contour changes of the glass panel.

While the present inventionhas been shown in a few forms only, it will be obvious to those skilled in the art that it is not so'limited, but that it is suspectible of various changes and modifications both in structure and in materials without departing from the spirit and scope thereof.

We claim as our invention:

1. A cathode ray tube including an envelope member, said envelope member being comprised of a face-plate portion and a funnel portion, said funnel portion being comprised of a flared portion and a neck portion, an electron beam generating means positioned within the neck portion of said envelope member, a luminescent screen positioned adjacent said face plate portion, a shadow mask electrode having a plurality of apertures therein positioned between said luminescent screen and said electron beam generating means and a thin flexible metallic electron beam shield member positioned between said shadow mask electrode and said electron beam generating means and positioned adjacent said envelope member, said'lectronbeam shield member being comprised o'f aluminum foil material.

2. In a cathode ray tube having an envelope memher, a "shadow mask:electrode and aluminescent screen, an electron beam shield member comprising a thin, flexi- 6 References Cited in the file of this patent UNITED STATES PATENTS Beckers Dec. 1, 1953 Fyler et al. Sept. 28, 1954 Lawrence Nov. 23, 1954 Law Nov. 1, 1955 McQuillen et al. Sept. 10, 1957 

